| Summary: | Background: Autoimmune bullous dermatoses present with overlapping clinical features that require histopathological correlation. Immunofluorescence is the most routinely used reliable investigation for diagnosis but requires specialised equipment and is technically sophisticated. Collagen IV immunohistochemistry is reported as a reliable test for the diagnosis of epidermolysis bullosa acquisita whereby It stains the roof of a subepidermal blister and would be expected on the floor in bullous pemphigoid. This technique could be performed as an easily accessible alternative to direct immunofluorescence and has been used anecdotally at our hospital. Aim: To investigate whether collagen IV immunohistochemistry can be used as a reliable histopathological confirmation of bullous pemphigoid. Methods: Two major investigations: 1. A systematic literature search was undertaken of all studies describing the use of collagen IV immunohistochemistry and those comparing it with immunofluorescence in the diagnosis of bullous pemphigoid. 2. A retrospective study of patients diagnosed with bullous pemphigoid over 12 years seen at Groote Schuur Hospital was performed. Patient records that had results for both direct immunofluorescence and collagen IV immunohistochemistry were selected. The positive percentage agreement was calculated. Results: 1. Two studies were found that investigated the use of collagen IV immunohistochemistry in bullous pemphigoid. All reported 33 (100%) cases demonstrated collagen IV at the floor of a subepidermal blister. Of these, 25/25 cases were in agreement with direct immunofluorescence and 7/8 with indirect immunofluorescence which were used as reference standard investigations. 2. In this study, collagen IV was positive in 96% (79/82) of cases and direct immunofluorescence was positive in 85% (72/82) of cases. A positive percentage agreement of 80.5% suggested a strongly positive test accordance. Limitations: 1. The literature search was limited to articles written in english only. 2. The retrospective design and the lack of controls without bullous pemphigoid made it impossible to calculate sensitivity and specificity as well as the kappa statistic. Conclusion: Collagen IV immunohistochemistry is a valid, simple and widely available test which demonstrates accordance with routinely used direct immunofluorescence in the confirmation of bullous pemphigoid. Through clinical and histomorphological correlation, it may be a useful test in resourcelimited settings without facilities for direct immunofluorescence. However, larger controlled studies are warranted to confirm this.
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